This invention relates to reciprocating internal combustion engines and, in particular, to linkage arms connecting a piston to a crankshaft, in addition to the connecting rod, for preventing the piston from wobbling within its cylinder.
As known in the prior art, an internal combustion engine comprises one or more right circular cylinders each containing a piston closely fitting but movable within the cylinder. One end of the cylinder is closed, forming a combustion chamber. The piston typically has several resilient rings in parallel grooves about its circumference for providing a gas-tight, sliding seal between the closed, upper portion of the cylinder and the lower portion of the cylinder. The piston is typically hollow to reduce the mass thereof, resembling an inverted cup. The lower end of the cup is called the skirt of the piston. A wrist pin extends across the diameter of the skirt. Work is obtained from the piston by means of a rotating crankshaft and a connecting rod joining the crankshaft to the wrist pin.
In operation, the crankshaft rotates and the connecting rod oscillates about the wrist pin in a pendulum motion. Because of viscous forces, there is a small but finite moment exerted on the piston by the connecting rod and wrist pin, tending to rotate the piston about the axis of the wrist pin. This wobble or rocking of the piston can cause significantly increased wear of the cylinder because the square edges of the rings, and of the piston itself, engage the sparsely lubricated upper end of the cylinder and act as a chisel, causing what is known as adhesive wear.
This wear causes the cylinder to become out of true and out of round. That is, the cylinder is no longer a right circular cylinder but the frustrum of a cone with the larger opening away from the crankshaft. A cross section of the cylinder is no longer circular but oval or elliptical with the minor axis of the ellipse parallel to the axis of the wrist pin. This wear pattern is characteristic of wobble or rocking about the axis of the wrist pin and is in addition to the normal wear of the rings on the wall of the cylinder. This out of roundness and taper is a major cause of the loss of the gas tight seal across the rings. In an internal combustion engine, this causes loss of compression (and loss of power) and burning of oil vapor drawn into the cylinder from the crankcase.
In automobile engines, whether gasoline fueled or diesel, the wear is tolerated to the extent that the time it takes for the wear to become a problem exceeds the typical lifetime of the vehicle. For trucks, locomotives, marine or fixed engines, this is not the case at all. The wear from the wobble of the piston reduces the time between overhauls of the engine. The time and cost of an overhaul are considerable. Thus, it is highly desirable to increase the time between such services. Further, on some engines, the distortion of the cylinder requires installation of new sleeve inserts for each cylinder in order to render the cylinder true and round. On other engines, material must be removed from the cylinder, in addition to what had been worn away, in order to correct the cylinder. This reduces the number of times that such engines can be overhauled. In both cases, the overhaul is expensive.
There are two basic solutions in the prior art to the problem of piston wobble or rocking. One solution is to lengthen the skirt of the piston. By using a longer piston, one obtains a more stable piston. However, a longer skirt decreases the arc through which the connecting rod can oscillate, requiring either a shorter stroke on the crankshaft or a longer connecting rod; the latter greatly increasing the size of the engine. A longer skirt also increases fluid dynamic drag and increases power loss.
The second solution is a carryover from the days of steam engines in which a crosshead member was interposed between the working piston and the crankshaft. The working piston and the crosshead member were connected by a shaft
passing through a bearing which sealed the cylinder. In U.S. Pat. No. 2,395,911, a stabilizing shaft extends downwardly from the piston and engages a bearing supported by a crossmember. A split connecting rod straddles the stabilizing shaft, connecting the wrist pin with the crankshaft. While reducing piston wobble, this approach requires a considerably larger crankcase, which may not be acceptable.
In view of the foregoing, it is therefore an object of the invention to provide an improved means for stabilizing a piston within a cylinder.
Another object of the invention is to increase the service life of internal combustion engines.
A further object of the invention is to minimize distortion of the cylinder due to wear.
Another object of the invention is to increase the number of times that an engine can be overhauled.